Relationships between brain water content and diffusion tensor imaging parameters (apparent diffusion coefficient and fractional anisotropy) in multiple sclerosis

Fifteen multiple sclerosis patients were examined by diffusion tensor imaging (DTI) to determine fractional anisotropy (FA) and apparent diffusion coefficient (ADC) in a superventricular volume of interest of 8×8×2 cm³ containing gray matter (GM) and white matter (WM) tissue. Point resolved spectroscopy 2D-chemical shift imaging of the same volume was performed without water suppression. The water contents and DTI parameters in 64 voxels of 2 cm³ were compared. The water content was increased in patients compared with controls (GM: 244±21 vs. 194±10 a.u.; WM: 245±32 vs. 190±11 a.u.), FA decreased (GM: 0.226±0.038 vs. 0.270±0.020; WM: 0.337±0.044 vs. 0.402±0.011) and ADC increased [GM: 1134±203 vs. 899±28 (×10⁻⁶ mm²/s); WM: 901±138 vs. 751±17 (×10⁻⁶ mm²/s)]. Correlations of water content with FA and ADC in WM were strong (r=−0.68, P<0.02; r=0.75; P<0.01, respectively); those in GM were weaker (r=−0.50, P<0.05; r=0.45, P<0.1, respectively). Likewise, FA and ADC were more strongly correlated in WM (r=−0.88; P<0.00001) than in GM (r=−0.69, P<0.01). The demonstrated relationship between DTI parameters and water content in multiple sclerosis patients suggests a potential for therapy monitoring in normal-appearing brain tissue.